Movatterモバイル変換

Internet Engineering Task Force (IETF)                          J. AbleyRequest for Comments: 6305                                         ICANNCategory: Informational                                         W. MatonISSN: 2070-1721                                                 NRC-CNRC                                                               July 2011I'm Being Attacked by PRISONER.IANA.ORG!Abstract   Many sites connected to the Internet make use of IPv4 addresses that   are not globally unique.  Examples are the addresses designated inRFC 1918 for private use within individual sites.   Hosts should never normally send DNS reverse-mapping queries for   those addresses on the public Internet.  However, such queries are   frequently observed.  Authoritative servers are deployed to provide   authoritative answers to such queries as part of a loosely   coordinated effort known as the AS112 project.   Since queries sent to AS112 servers are usually not intentional, the   replies received back from those servers are typically unexpected.   Unexpected inbound traffic can trigger alarms on intrusion detection   systems and firewalls, and operators of such systems often mistakenly   believe that they are being attacked.   This document provides background information and technical advice to   those firewall operators.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6305.Abley & Maton                 Informational                     [Page 1]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1.  Introduction and Target Audience  . . . . . . . . . . . . . . .32.  Private-Use Addresses . . . . . . . . . . . . . . . . . . . . .33.  DNS Reverse Mapping . . . . . . . . . . . . . . . . . . . . . .34.  DNS Reverse Mapping for Private-Use Addresses . . . . . . . . .45.  AS112 Nameservers . . . . . . . . . . . . . . . . . . . . . . .46.  Inbound Traffic from AS112 Servers  . . . . . . . . . . . . . .57.  Corrective Measures . . . . . . . . . . . . . . . . . . . . . .58.  AS112 Contact Information . . . . . . . . . . . . . . . . . . .69.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .610. Security Considerations . . . . . . . . . . . . . . . . . . . .711. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .712. References  . . . . . . . . . . . . . . . . . . . . . . . . . .712.1.  Normative References . . . . . . . . . . . . . . . . . . .712.2.  Informative References . . . . . . . . . . . . . . . . . .7Abley & Maton                 Informational                     [Page 2]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 20111.  Introduction and Target Audience   Readers of this document may well have experienced an alarm from a   firewall or an intrusion-detection system, triggered by unexpected   inbound traffic from the Internet.  The traffic probably appeared to   originate from one of several hosts discussed further below.   The published contacts for those hosts may well have suggested that   you consult this document.   If you are following up on such an event, you are encouraged to   follow your normal security procedures and take whatever action you   consider to be appropriate.  This document contains information that   may assist you.2.  Private-Use Addresses   Many sites connected to the Internet make use of address blocks   designated in [RFC1918] for private use.  One example of such   addresses is 10.1.30.20.   Because these ranges of addresses are used by many sites all over the   world, each individual address can only ever have local significance.   For example, the host numbered 192.168.18.234 in one site almost   certainly has nothing to do with a host with the same address located   in a different site.3.  DNS Reverse Mapping   The Domain Name System (DNS) [RFC1034] can be used to obtain a name   for a particular network address.  The process by which this happens   is as follows:   1.  The network address is rearranged in order to construct a name       that can be looked up in the DNS.  For example, the IPv4 address       10.1.30.20 corresponds to the DNS name 20.30.1.10.IN-ADDR.ARPA.   2.  A DNS query is constructed for that name, requesting a DNS record       of the type "PTR".   3.  The DNS query is sent to a resolver.   4.  If a response is received in response to the query, the answer       will typically indicate either the hostname corresponding to the       network address, or the fact that no hostname can be found.   This procedure is generally carried out automatically by software,   and hence is largely hidden from users and administrators.Abley & Maton                 Informational                     [Page 3]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 2011   Applications might have reason to look up an IP address in order to   gather extra information for a log file, for example.4.  DNS Reverse Mapping for Private-Use Addresses   As noted inSection 2, private-use addresses have only local   significance.  This means that sending queries out to the Internet is   not sensible: there is no way for the public DNS to provide a useful   answer to a question that has no global meaning.   Despite the fact that the public DNS cannot provide answers, many   sites have misconfigurations in the way they connect to the Internet;   this results in such queries relating to internal infrastructure   being sent outside the site.  From the perspective of the public DNS,   these queries are junk -- they cannot be answered usefully and result   in unnecessary traffic being received by the nameservers which   underpin the operation of the reverse DNS (the so-called reverse   servers [RFC5855], which serve "IN-ADDR.ARPA").   To isolate this traffic and reduce the load on the rest of the   reverse DNS infrastructure, dedicated servers have been deployed in   the Internet to receive and reply to these junk queries.  These   servers are deployed in many places in a loosely coordinated effort   known as the "AS112 project".  More details about the AS112 project   can be found at <http://www.as112.net/>.5.  AS112 Nameservers   The nameservers responsible for answering queries relating to   private-use addresses are as follows:   o  PRISONER.IANA.ORG (192.175.48.1)   o  BLACKHOLE-1.IANA.ORG (192.175.48.6)   o  BLACKHOLE-2.IANA.ORG (192.175.48.42)   A request sent to one of these servers will result in a response   being returned to the client.  The response will typically be a UDP   datagram, although it's perfectly valid for requests to be made over   TCP.  In both cases, the source port of packets returning to the site   that originated the DNS request will be 53.Abley & Maton                 Informational                     [Page 4]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 20116.  Inbound Traffic from AS112 Servers   Where firewalls or intrusion detection systems (IDSs) are configured   to block traffic received from AS112 servers, superficial review of   the traffic may seem alarming to site administrators.   o  Since requests directed ultimately to AS112 servers are usually      triggered automatically by applications, review of firewall logs      may indicate a large number of policy violations occurring over an      extended period of time.   o  Where responses from AS112 servers are blocked by firewalls, hosts      will often retry, often with a relatively high frequency.  This      can cause inbound traffic to be misclassified as a denial-of-      service (DoS) attack.  In some cases, the source ports used by      individual hosts for successive retries increase in a predictable      fashion (e.g. monotonically), which can cause the replies from the      AS112 server to resemble a port scan.   o  A site administrator may attempt to perform active measurement of      the remote host in response to alarms raised by inbound traffic,      e.g. initiating a port scan in order to gather information about      the host which is apparently attacking the site.  Such a scan will      usually result in additional inbound traffic to the site      performing the measurement, e.g., an apparent flood of ICMP      messages that may trigger additional firewall alarms and obfuscate      the process of identifying the originally problematic traffic.7.  Corrective Measures   A site that receives responses from one of the nameservers listed inSection 5 is probably under no immediate danger, and the traffic   associated with those responses probably requires no emergency action   by the site concerned.  However, this document cannot aspire to   dictate the security policy of individual sites, and it is recognised   that many sites will have perfectly valid policies that dictate that   corrective measures should be taken to stop the responses from AS112   servers.   It should be noted, however, that the operators of AS112 nameservers,   which are generating the responses described in this document, are   not ultimately responsible for the inbound traffic received by the   site: that traffic is generated in response to queries that are sent   out from the site, and so the only effective measures to stop the   inbound traffic is to prevent the original queries from being made.Abley & Maton                 Informational                     [Page 5]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 2011   Possible measures that might be taken to prevent these queries   include:   1.  Stop hosts from making these DNS reverse-mapping queries in the       first place.  In some cases, servers can be configured not to       perform DNS reverse-mapping lookups, for example.  As a general       site-wide approach, however, this measure is frequently difficult       to implement due to the large number of hosts and applications       involved.   2.  Block DNS reverse-mapping queries to the AS112 servers from       leaving the site using firewalls between the site and the       Internet.  Although this might appear to be sensible, such a       measure might have unintended consequences: the inability to       receive an answer to DNS reverse-mapping queries might lead to       long DNS lookup timeouts, for example, which could cause       applications to malfunction.  (It may also lead to the belief       that the Internet or the local network is down.)   3.  Configure all DNS resolvers in the site to answer authoritatively       for the zones corresponding to the private-use address blocks in       use.  This should prevent resolvers from ever needing to send       these queries to the public DNS.  Guidance and recommendations       for this aspect of resolver configuration can be found in       [RFC6303].   4.  Implement a private AS112 node within the site.  Guidance for       constructing an AS112 node may be found in [RFC6304].8.  AS112 Contact Information   More information about the AS112 project can be found at   <http://www.as112.net/>.9.  IANA Considerations   The AS112 nameservers are all named under the domain IANA.ORG (seeSection 5).  The IANA is the organisation responsible for the   coordination of many technical aspects of the Internet's basic   infrastructure.  The AS112 project nameservers provide a public   service to the Internet that is sanctioned by and operated in loose   coordination with the IANA.Abley & Maton                 Informational                     [Page 6]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 201110.  Security Considerations   The purpose of this document is to help site administrators properly   identify traffic received from AS112 nodes and to provide background   information to allow appropriate measures to be taken in response to   it.   Hosts should never normally send queries to AS112 servers: queries   relating to private-use addresses should be answered locally within a   site.  Hosts that send queries to AS112 servers may well leak   information relating to private infrastructure to the public network;   this could represent a security risk.11.  Acknowledgements   The authors wish to acknowledge the assistance of S. Moonesamy in the   preparation of this document.12.  References12.1.  Normative References   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",              STD 13,RFC 1034, November 1987.   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and              E. Lear, "Address Allocation for Private Internets",BCP 5,RFC 1918, February 1996.12.2.  Informative References   [RFC5855]  Abley, J. and T. Manderson, "Nameservers for IPv4 and IPv6              Reverse Zones",BCP 155,RFC 5855, May 2010.   [RFC6303]  Andrews, M., "Locally Served DNS Zones",BCP 163,RFC 6303, July 2011.   [RFC6304]  Abley, J. and W. Maton, "AS112 Nameserver Operations",RFC 6304, July 2011.Abley & Maton                 Informational                     [Page 7]

RFC 6305        I'm Being Attacked by PRISONER.IANA.ORG!       July 2011Authors' Addresses   Joe Abley   ICANN   4676 Admiralty Way, Suite 330   Marina del Rey, CA  90292   US   Phone: +1 519 670 9327   EMail: joe.abley@icann.org   William F. Maton Sotomayor   National Research Council of Canada   1200 Montreal Road   Ottawa, ON  K1A 0R6   Canada   Phone: +1 613 993 0880   EMail: wmaton@ryouko.imsb.nrc.caAbley & Maton                 Informational                     [Page 8]